This invention relates to a process for forming a pattern film for use, for example, in correcting or repairing a photomask during the fabrication of semiconductor devices.
Masks and reticles for use in the manufacture of semiconductors are made by etching patterns by exposure to light. The process presents problems because of the defects the patterns tend to develop. These defects are classified into two groups; unwanted pattern portions left unremoved, which are called black-spot defects, and portions needed but unintentionally etched away, called clear or white-spot defects. Of these defects, those of the white-spot type are repaired by the use of an organic compound and irradiation with an ion beam. This has been carried out in varied ways which have been proposed up to now and which are broadly of two types.
One typical process consists of applying an organic film, such as photoresist, to the mask, and then irradiating each portion which has a white-spot defect with a focused ion beam to thereby polymerize or carbonize the irradiated portions of the organic film. The film portion polymerized or carbonized in this manner possesses excellent light-blocking and adhesion strength properties which render it suitable as a material for correcting white-spot defects. The process has drawbacks, however, including the need for the time-consuming step of applying the organic film and the necessity of using equipment large enough to handle the high energy, well in excess of 100 KeV, of the focused ion beam required for the irradiation.
The other process, developed by the present applicants and described in published Japanese Patent Application No. 58-201764 (Laid-Open No. 60-94728), involves directing a vapor stream of an organic compound at the surface of each white-spot defect and concurrently irradiating the surface with a focused ion beam, whereby the organic compound molecules are polymerized or carbonized to form a solid deposit on the defective portion. The second process has advantages over the first one described in that it eliminates the separate step of applying an organic film, and the equipment is simplified because of a lower energy requirement, i.e., below 30 keV, for the acceleration of the ions needed for irradiation. The kinds or organic compounds thus far proposed for use in known processes of the second type have included vacuum pump oils, organometallic compounds such as trimethylaluminum, and dibenzene complexes such as [Cr(C.sub.6 H.sub.6).sub.2 ].
When vacuum pump oil is used in remedying white-spot defects, its low vapor pressure at ordinary temperature, i.e., below 10.sup.-6 Torr, makes the supply of the oil molecules insufficient for film formation by polymerization or carbonization; consequently, the rate of film buildup to a desired thickness is low. If the vacuum pump oil is heated to raise its vapor pressure for a faster increase in film thickness, it condenses on the substrate surface. The condensate then gives incompletely polymerized or cabonized portions along the edges between the ion-beam-irradiated and the non-irradiated areas, causing difficulty in film formation and other undesired effects.
The pattern-film forming processes using organometallic compounds and dibenzene complexes also have drawbacks. When the vapor pressure in the vicinity of the substrate is low, the buildup of the film layer progresses slowly, and attempts to raise the pressure in order to attain an adequately rapid film buildup will lead to difficulties such as the scattering of the ion beam causing it to go out of focus, an added load upon the vapor discharge system, and adverse effects upon the ion source. Furthermore, the organic compounds containing metal atoms which are typically used are often so toxic or unstable that they pose handling problems.